A liquid crystal display device is widely used for a display of a personal computer, a television and so forth. The device utilizes optical anisotropy, dielectric anisotropy and so forth of a liquid crystal compound. As an operating mode of the liquid crystal display device, a variety of modes are known, such as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the IPS mode, the FFS mode and the VA mode are known to improve narrowness of a viewing angle, being a disadvantage of operating modes such as the TN mode and the STN mode. In the liquid crystal display device having the mode of the kind, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the liquid crystal display device, a liquid crystal compound contained in the composition preferably has preferably physical properties described in the following (1) to (8):
(1) high stability to heat, light and so forth;
(2) a high clearing point;
(3) a low minimum temperature of a liquid crystal phase;
(4) small viscosity (η);
(5) suitable optical anisotropy (Δn);
(6) large negative dielectric anisotropy (Δ∈);
(7) a suitable elastic constant (K33: bend elastic constant); and
(8) excellent compatibility with other liquid crystal compounds.
An effect of the physical properties of the liquid crystal compound on the characteristics of the device is as described below. A compound having the high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes longer. A compound having the high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having the low minimum temperature of the liquid crystal phase such as a nematic phase and a smectic phase, as described in (3), in particular, a compound having the low minimum temperature of the nematic phase, also extends the temperature range in which the device can be used. A compound having the small viscosity as described in (4) decreases a response time of the device.
A compound having the suitable optical anisotropy as described in (5) improves contrast of the device. According to a design of the device, a compound having a large optical anisotropy or a small optical anisotropy, more specifically a compound having the suitable optical anisotropy is required. When decreasing the response time by decreasing a cell gap of the device, a compound having the large optical anisotropy is suitable. A compound having the large negative dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device is decreased.
With regard to (7), a compound having the large elastic constant decreases the response time of the device. A compound having the small elastic constant decreases the threshold voltage of the device. Therefore, a suitable elastic constant is required according to characteristics that are desirably improved. A compound having the excellent compatibility with other liquid crystal compound as described in (8) is preferred. The reason is that the physical properties of a composition are adjusted by mixing liquid crystal compounds that have different physical properties.
A variety of liquid crystal compounds having the large negative dielectric anisotropy have so far been prepared (for example, Patent literature No. 1). Patent literature No. 1 discloses compound (C-1). However, compound (C-1) has neither sufficiently high clearing point nor sufficiently high compatibility with other compounds.

In view of such a situation, development has been desired for a compound having excellent physical properties and a suitable balance regarding the physical properties with regard to (1) to (8) as described above. In particular, a compound having the large negative dielectric anisotropy, the high clearing point and the high compatibility with other compounds has been required.